It is now well established that our nation, and many other nations, face serious environmental and fuel supply problems with internal combustion engines. Most internal combustion engines run on either gasoline or diesel fuels, both of which are petroleum products. As is well known, the world's oil supply is generally found far beneath the planet's surface, and in only a few specific locations. Enormous amounts of infrastructure and significant costs are involved in finding, extracting, and processing the oil into gasoline and diesel fuels, and further significant costs are incurred in the storage, transportation, and sale of the finished gasoline and diesel fuel products.
It is well established that there is only a finite supply of petroleum in our world, and further that the byproducts of combustion, among them carbon monoxide (CO), can and have caused environmental damage to our planet, and have created health risks to humans as well. Thus our nation, as well as many others, faces the problems of a strong reliance on petroleum products for transportation, heating and manufacturing, and that those petroleum products are in short supply and damaging our world and ourselves.
As a result, there is increased attention on lessening both the reliance on petroleum products and on the negative effects of burning petroleum products. A partial solution is the use of electric vehicles. Electric vehicles, whether purely electric or in the form of gasoline-electric hybrid vehicles, will reduce pollution and the use of petroleum products, especially in the form of gasoline since most electricity-producing power plants run on either natural gas, oil, nuclear power, or coal. While each of these alternative fuel sources produces its own set of issues in regard to the environmental and supply debate, it is generally believed that if a nation, in particular the United States of America, could replace significant amounts of its internal combustion automobile engines with electric vehicles, local, national and perhaps global pollution levels would decrease.
There have been, therefore, significant expenditures of time, effort, and financial resources to launch the use of at least gasoline-electric hybrid (herein after “hybrid”) vehicles, as well as vehicles that run exclusively on electricity (herein after, both types of automobiles shall be referred to simply as “electric vehicles”), by private automobile manufacturers, and government leaders. Of the many obstacles that have presented themselves to those in the industry of manufacturing electric vehicles, one significant problem is that of recharging the batteries, cells, or other electrical energy storage devices.
Vehicle energy storage systems are normally recharged using direct contact conductors between an alternating current (AC) source such as is found in most homes in the form or electrical outlets; nominally 120 or 240 VAC. A well known example of a direct contact conductor is a two or three pronged plug normally found with any electrical device. Manually plugging a two or three pronged plug from a charging device to the electric automobile requires that conductors carrying potentially lethal voltages be handled. In addition, the conductors may be exposed, tampered with, or damaged, or otherwise present hazards to the operator or other naïve subjects in the vicinity of the charging vehicle. Although most household current is about 120 VAC single phase, in order to recharge electric vehicle batteries in a reasonable amount of time (two-four hours), it is anticipated that a connection to a 240 VAC source would be required because of the size and capacity of such batteries. Household current from a 240 VAC source is used in most electric clothes dryers and clothes washing machines. The owner/user of the electric vehicle would then be required to manually interact with the higher voltage three pronged plug and connect it at the beginning of the charging cycle, and disconnect it at the end of the charging cycle. The connection and disconnection of three pronged plugs carrying 240 VAC presents an inconvenient and potentially hazardous method of vehicle interface, particularly in inclement weather.
In order to alleviate the problem of using two or three pronged conductors, exemplary embodiments of the present invention utilize an inductive charging system to transfer power to the electric vehicle. Inductive charging, as is known to those of skill in the art, utilizes a transformer to charge the battery of the target device. One example of known inductive charging systems is that used to charge electric toothbrushes.
Some electric toothbrushes use non-rechargeable batteries, some use rechargeable batteries that are physically connected to two or more external connectors that interface with matching connectors on a base station. But in an inductive recharging system for an electric toothbrush, there are no such external connects. Instead, a first transformer in the base receives the primary voltage from either a wall source, or a stepped down voltage from some internal circuitry, and creates a time-varying magnetic field through the effect of a ferro-magnetic iron core used in the base transformer. The time-varying magnetic field permeates into the secondary transformer core in the electric toothbrush, and a time-varying voltage is produced on the windings that surround the secondary transformer core. This voltage is fed to internal circuitry where it is rectified and filtered and then input to the battery to recharge it. The same general principles apply to electric vehicle inductive charging systems.
One item briefly discussed above is the time varying aspect of the AC voltage, and hence the time-varying aspect of the magnetic fields in both the primary and secondary transformer cores. Typically, house current in the U.S. operates at about 60 hertz (Hz), or cycles per second. The problem with using a voltage that oscillates at 60 Hz, is that the size of the components in an inductive charging system is inversely proportional to the frequency, and thus the lower the frequency of the voltage, the greater the size of the inductive charging system. As those of ordinary skill in the automotive industry can attest, size is extremely critical to vehicle manufacturers because it is very important to automotive owners. The size and weight of an object directly affects the fuel mileage of the vehicle. Thus in other inductive charging systems, high frequency voltages, normally above 10 kHz, have been used to transfer power by radiation and tuned coils. There is, however, a cost associated with the use of higher frequency voltages and that is the subsequent loss of efficiency. The higher the frequency at which the charging system operates, the less efficient is the charging system. A less efficient charging system means that much more power must be input into the primary side of the recharging system resulting in greater cost.